1. Field of the Invention
The present invention relates to an ink-jet recording head provided with a filter and a method for manufacturing the same. In particular, the present invention relates to an ink-jet recording head provided with an ink supply hole penetrating from a bottom surface to a top surface of a substrate including a plurality of ejection nozzles and a method for manufacturing the ink-jet recording head.
2. Description of the Related Art
Known ink-jet recording heads can form fine ink droplets by downsizing ejection nozzles to eject ink, and have become mainstream photorealistic printers in recent years. However, as ejection nozzles become finer, a problem of clogging of the ejection nozzle occurs due to dust contained in ink.
Consequently, ink-jet recording heads incorporating filters to remove the dust have been developed.
FIG. 1 is a sectional side view showing an example of a known ink-jet recording head provided with a filter.
An ink-jet recording head 420 includes electrothermal conversion elements, although not shown in the drawing, which generate thermal energy to initiate film boiling of ink in accordance with electric signals, in an ink flow path 415; ejection nozzles 411 to eject ink, located at positions in accordance with electrothermal conversion elements; an ink supply hole 412 to supply ink from an ink tank to the ink flow path 415; and a columnar filter 404 disposed in the ink flow path 415. As shown in FIGS. 2A-C, this filter 404 is disposed in such as manner that a spacing A in the filter 404 is smaller than or equal to a maximum linear distance between intersection points of a straight line passing through the geometric center of the ejection nozzle 411 and an edge of the ejection nozzle 411 in a plan view when viewed from an ejection nozzle surface (top surface) side. That is, in the configuration shown in FIGS. 2A-C, since the ejection nozzle is circular, the geometric center of the ejection nozzle 411 is the center of the circle. Therefore, a straight line passing through this center and having a maximum distance between points of intersection with the circumference of the circle of the ejection nozzle 411 refers to a diameter (refers to a major axis when the ejection nozzle 411 is elliptical, for example). Accordingly, the filter 404 is disposed such that the spacing A is smaller than or equal to the diameter A′ of the ejection nozzle 411.
With respect to the filter 404 in which columns are set up in the ink flow path 415, when the two-dimensional relationship between positions is viewed from the top surface, the spacing A shown in FIGS. 2A-C is smaller than or equal to the diameter of the ejection nozzle 411. However, in the recording head which ejects fine droplets, even when the diameter of an ejection nozzle is reduced, it is difficult to correspondingly decrease the ink flow path height B because the performance of refilling ink must be maintained. Consequently, when such a recording head is viewed from the direction indicated by an arrow D shown in FIG. 2B, since the height B of the ink flow path 415 is larger than the spacing A in the filter 404, as shown in FIG. 2C, if slim dust flows into the ink flow path 415 while being vertically oriented, the dust passes through the filter 404. However, the dust cannot be ejected through the ejection nozzle 411, so that non-ejection of the ink may result.
On the other hand, schemes to prevent the entrance of dust may be devised. A component provided with fine holes may be attached to an ink supply hole for supplying ink to a plurality of ink flow paths, or a part of an ink flow path may be processed to have through holes.
For example, Japanese Patent Laid-Open No. 5-254120 discloses a method, in which fine through holes are formed by downstream processing in appropriate portions of an ink flow path and a liquid chamber. In this method, a component having an adequate strength to form the ink flow path and the liquid chamber is required. In general, laser processing is used for boring through holes therein. However, when the downstream processing is performed by laser processing or other means, dust may enter into the ink flow path and the liquid chamber during the formation of through holes in the component. As a result, since the dust cannot be taken out because of the characteristic of the through holes (filter), a cause of non-ejection of ink may be generated defying expectations.
Japanese Patent Laid-Open No. 5-208503 (corresponding U.S. Pat. No. 5,141,596) discloses a method, in which silicon is subjected to ion implantation and, thereby, a portion sensitive to etching and a portion resistant to etching are formed, so that an ink supply hole and an ink chamber are formed and, at the same time, through holes are bored, the through holes having a dimension smaller than or equal to a minimum distance between two intersection points of a straight line passing through the geometric center of the ejection nozzle and a circumference of the above-described ejection nozzle.
However, in this method, since the area of the through holes are determined based on the diffusion of ions, the concentration due to diffusion does not become two values corresponding to a portion sensitive to etching and a portion resistant to etching, but there are gradations in concentration. Therefore, the size of the through holes cannot be precisely controlled. Since anisotropic etching is performed from a surface opposite to the surface to be provided with through holes, if the area of the portion provided with through holes (filter) is increased, the area to become a liquid chamber is increased and, therefore, the formation becomes difficult. Therefore, the area of the portion to be provided with the through holes is restricted. The portion to be provided with the through holes becomes very narrow since the formation is performed by anisotropic etching of silicon. Consequently, when solid printing or the like in which ink is ejected from a plurality of ejection nozzles is performed, a pressure drop is increased and, therefore, high-speed printing becomes difficult. Furthermore, since the liquid chamber is disposed, alignment is required for joining to a wafer including ejection nozzles.
Japanese Patent Laid-Open No. 2000-094700 discloses that the above-described fine through holes are formed in a portion having a large area. However, since the formation of an ink supply hole is performed simultaneously, an etching solution for forming the ink supply hole must be penetrated through the fine through holes, and when a mold material for the ink flow path is removed, the mold material for the ink flow path must be fused and removed under the condition in which both the ejection nozzle and the through holes are small holes. Therefore, the operability of the removal is poor, and this method is impractical.